BRUSSELS – The European Union plans to lodge a case with the World Trade Organization against Chinese duties on imports of stainless steel tubes, EU sources said on Tuesday, opening another front in a rapidly escalating trade conflict with Beijing.

The move will allow the EU to join a complaint against China filed by Japan in December.

The EU complaint would seek to overturn China's duties on exports of seamless steel tubes made by firms such as Spain's Tubacex S.A and Germany's Salzgitter A.G , the sources said. The sources asked not to be identified because of the sensitivity of the case.

The filing, which may come as soon as Thursday or Friday, will send a signal to China that the EU is willing to take legal action against any duties it considers to be based on retaliation rather than objective evidence.